Primary transfer sub for dual concentric drillpipe

ABSTRACT

A downhole transfer sub for use with dual concentric drillstring and rotary drilling apparatus and a downhole percussion motor. The transfer sub, positoned immediately above the downhole percussion motor, transfers the downstream drilling fluid from the annular space in the double-wall drillpipe to the inlet bore of the downhole percussion motor, and also transfers the upstream exhausted fluid and entrained cuttings from the bottom of the borehole to the central bore of the double-wall drillpipe for return to the ground surface. Alternatively, the drill may be operated as a rotary drill with downhole percussion motor removed, in which case the transfer sub will be direct-connected at its lower end to a conventional rotary bit.

[ July 24, 1973 PRIMARY TRANSFER SUB FOR DUAL CONCENTRIC DRILLPIPE 175/92, 101, 106, 102, 324, 320, 60; 205/133 A, 133 R, 332.2, 332.3, 53.47; 166/65 R [56] References Cited UNITED STATES PATENTS 2,849,214 8/1958 Hall 175/215 X 3,170,520 2/1965 Arutunoff 166/65 R 3,297,100 l/l967 Crews 175/215 X 3,323,604 6/1967 l-lenderson.. 175/215 X 3,489,438 1/1970 McClure 175/215 X 3,667,555 6/1972 Elenburg 175/60 Primary Examiner-David H. Brown Attorney-John E. Prothroe 57 ABSTRACT A downhole transfer sub for use with dual concentric drillstring and rotary drilling apparatus and a downhole percussion motor. The transfer sub, positoned immediately above the downhole percussion motor, transfers the downstream drilling fluid from the annular space in the double-wall drillpipe to the inlet bore of the downhole percussion motor, and also transfers the upstream exhausted fluid and entrained cuttings from the bottom of the borehole to the central bore of the double-wall drillpipe for return to the ground surface. Alternatively, the drill may be operated as a rotary drill with downhole percussion motor removed, in which case the transfer sub will be direct-connected at its lower end to a conventional rotary bit.

14 Claims, 6 Drawing Figures PRIMARY TRANSFER SUB FOR DUAL CONCENTRIC DRILLPIPE This invention relates to new and useful improvements in borehole drilling appratus, and, more particularly, to drilling apparatus in which concentric doublewall drillpipe is employed, in which fluid under pressure, such as air, is circulated in the double-wall drillpipe, downwardly through the annulus, to recover cuttings from the bottom of the borehole, for transmission to the ground surface through the inner pipe. In certain of its aspects, the present invention relates to improvements in dual concentric drillpipe dealt with in the Chapman US. Pat. application Ser. No. 207,758, filed Dec. 14, 1971, on DUAL CONCENTRIC DRILLPIPE.

Generally contemplated are new features of particular structural and operational advantage for incorporation in dual concentric drillpipe, for transferring the upward flow of drilling fluid and entrained rock cuttings from the annular space between the drillpipe and the bore of the hole, to the central passage of the dual concentric drillpipe, for upward transmission and delivery to the ground surface through the inner pipe, without significantly restricting the flow characteristics.

In co-pending Chapman US. Pat. application Ser. No. 207,758, filed Dec. 14, 1971, on DUAL CON- CENTRIC DRILLPIPE, the description has been established of drilling apparatus, utilizing dual string drillpipe, with downhole percussion motor, utilizing energized drilling fluid such as compressed gas or liquid under pressure, supplied at the surface of the ground to a rotary hydraulic motor, the fluid passing into the annulus between the inner and outer tubes by way of a packing gland assembly, then downwardly through the annular area between the inner and outer pipes and tool joints to the lower end of the drillstring, where a transfer assembly, known as a transfer sub positioned immediately above the downhle percussion motor, transfers the fluid stream to the inner tube, for delivery to the percussion motor. Energy from the fluid is then transferred to the percussion motor and bit face, for operation of the drill bit against the bottom of the borehole. The exhausted fluid then picks up the rock chip cuttings formed at the bit, for entrained upward flow past the percussion motor in the annulus formed between the percussion motor and the rock formation borehole wall, to the transfer sub, where the flow of fluid and entrained cuttings enters the transfer. sub by means of ports in the walls thereof which deliver the fluid flow and entrained cuttings to the bore of the inner tube. The flow of cuttings and exhaust fluid then continues upwardly through the inner tube to the ground surface. Alternatively, and particularly when the drill is penetrating soft strata, the drill may be operated as a rotary drill with the downhole percussion motor removed, in which case the transfer sub will be connected at its lower end directly to a conventional rotary bit and at its upper end to the depending end of the drillstring.

Fluid pressure is maintained in the annular space between the rock formation wall of the borehole and the outer pipe, by means of a surface seal assembly and a small downward fluid flow in this annular space, which directs the upward flow of exhausted fluid and entrained cuttings through the ports in the transfer sub into the bore of the inner concentric drill pipe.

The development of dual drillstring employing com pressed gas as the recovery fluid has necessitated solving various problems in order that a gas drilling system, as outlined, may become practical. One of the major problems encountered, and particularly with respect to the drilling of deeper boreholes, is the minimizing of pressure losses in the gas circuit in order to ensure adequate energy delivery at the downhole percussion motor, and also to assure the maintenance of sufficiently high upward gas velocities to entrain the cuttings throughout the course of the gas flow to the top of the borehole. This problem is not only acute in the design of drillpipe and pipe joints, as described in the said copending Champan US. Pat. application Ser. No. 207,758, filed Dec. 14, 1971 on DUAL CONCEN TRIC DRILLPIPE, but also in the design of the transfer sub, where the cross-sectional area of the entry ports and fluid passages must be maintained to minimize restriction in gas flow, while at the same time the transfer sub must develop the necessary physical strength to de liver torque on the drill bit and resist metal fatigue transmitted to the transfer sub as a result of the action of the downhole percussion motor.

In its broader aspect, the apparatus of the present in vention comprises a transfer sub for use with rotary drilling apparatus, having passages for downward flow of the energized drilling fluid, and interiorly thereof, an upward passage for the exhausted drilling fluid and entrained cuttings, in which the upper end of the transfer sub is equipped with a threaded dual-wall pipe joint, for removeable threaded connection to the lower end of the double-wall tubular concentric drillpipe, and in which the bottom end of the transfer sub comprises a single passage interiorly-threaded tool joint, for connection to the upper end of a downhole percussion motor or, alternatively, directly to a rotary rock bit, ports being provided through the dual walls of the transfer sub, to establish communication between the bore of the inner passage of the transfer sub and the exterior space surrounding. the transfer sub, such ports being of a design to minimize pressure loss in the upward flow of drilling fluid, the transfer sub developing adequate structural strengthto withstand the operational stresses developed by the rotary resistance of the bit, and the impact of the downhole percussion motor. The transfer sub is equipped at its lower end with a single opening, conventionally threaded box joint, for interconnection with a standard rotary bit. As will appear, the tool joint at the upper end of the transfer sub is so constructed that coupling rotation of the transfer sub with the lower end of the adjacent pipestand will simultaneously form two fluid-tight thread-coupled joints therebetween, connecting the inner and outer pipes respectively. The upper end tool joint on both the inner and outer members of the transfer sub is so constructed that when unacceptable wear occurs in the joint, it may be readily detached from the remainder of the transfer sub for replacement of the joint. A further particular advantage of the joint on the transfer sub of this invention is its capacity for sealing the inner joint without dependency on the inner members being in a predetermined made-up position, so that the inner joint is sealed at whatever condition happens to be the made-up condition of the outer threaded joint, within a relatively wide range of tolerance, while still developing the physical strength in the inner joint practically achievable only through the use of threads. Previously known dual-wall joints of similar construction have relied primarily on various combinations of threaded outer joints and telescopic inner joints in order to develop the required latitude of alignment, and to provide for differential expansion of the inner and outer pipes. This feature of the joints has been already described in detail in the Chapman U.S. Pat. application Ser. No. 207,758, filed Dec. 14, 1971, on DUAL CONCEN- TRIC DRILLPIPE.

An object of the present invention is to provide improved means whereby energized downstream drilling fluid, delivered from the annular space within a dualwall concentric drillstring, is transmitted to the inlet of a downhole percussion motor, or alternatively, directly to the central bore of a drill bit, and the exhaust air from the downhole motor and entrained cuttings produced at the drill bit are delivered to the bore of the interior pipe of the dual concentric drillstring.

A further object of this invention is the provision of improved drilling apparatus for use with dual-wall concentric drillpipe, for continuous downward transmission of drilling fluid in a plurality of first fluid passages, and the simultaneous upward transmission of exhaust drilling fluid and entrained cuttings through a second fluid passage, the exhaust air and entrained cuttings being admitted to the apparatus by means of ports passing through the walls thereof, isolated from the first fluid passages, whereby the exhaust air. and cuttings surrounding the apparatus are transferred laterally to the second fluid passage.

Another object of the present invention is to provide a transfer sub, as described, in which minimized pressure losses occur in the downstream energized drilling fluid delivered from the transfer sub to the downhole percussion motor and the exhaust drilling fluid, carrying entrained cuttings, delivered to the upstream passage of the dual-wall drillpipe and directed to the ground surface.

A still further object of the invention is to provide a transfer sub for threaded interconnection to the lower end of a drillstring, to which a rotary rock bit can be directly connected by means of a standard thread.

A still further object of the invention is the provision of a transfer sub which develops adequate physical strength to resist the severe torsional and impact stresses induced in the drilling operation.

Another object of the present invention is to provide a transfer sub which may be joined to the depending end of a dual-wall concentric drill-pipe, by means of a threaded joint on each of the outer and inner concentric tool joints, developing adequate physical strength and sealing the respective concentric tool joints against leakage of the contained pressurized fluid.

Other and more specific objects, features and advantages of the apparatus of this invention will appear from the detailed description hereinafter following, reference being had to the accompanying drawings which form a part of this disclosure and which illustrate,

merely by way of example, preferred forms of apparatus for the practice of this invention, which embodiments are illustrated in the accompanying drawings, in which:

FIG. 1 is a general view illustrating a complete dual concentric borehole drilling assembly, including drillstring, surface equipment, transfer sub and downhole percussion motor and drill bit;

FIG. 1A is a fragmentary view of a portion of the lower end of the drillstring depicted in FIG. I, with downhole percussion motor removed, and the transfer sub connected directly to the drill bit;

FIG. II is an enlarged longitudinal partially sectional view of the transfer sub, taken at line 2-2 of FIG. I;

FIG. III is a cross-sectional view of the transfer sub of FIG. II, taken at line 3-3 of FIG. II;

FIG. IV is an enlarged fragmentary section of the transfer sub, taken longitudinally through one of the lateral exhaust air and cuttings ports;

FIG. V is a longitudinal partially sectional view of the pin joint end of a stand of the dual-wall concentric drillpipe, interconnectable with the box joint end of the transfer sub.

In the drawings, like characters of reference indicate corresponding parts in the several figures.

STRUCTURE In the specific embodiment hereinafter described, the apparatus of this invention is used with dual concentric drilling apparatus in which a gaseous circulating fluid is employed, such as compressed air, which has been found to be highly satisfactory in drilling 'most solid mineral ground. It will be appreciated, however, that the apparatus of this invention may readily be used with dual concentric drillpipe employing other circulating fluids such as other gases, liquids, or combinations of'liquid and gas, depending on drilling conditions encountered.

Proceeding now to describe the invention in detail, reference should be made first to FIG. I, which generally illustrates the well drilling system employed with the apparatus of this invention, including surface equipment generally designated 10, drillstring gener ally designated 11, downhole percussion drilling motor generally designated at 12, transfer sub 27, drilling bit 13 and borehole 14.

The drill is desirably powered for rotary motion by a hydraulic motor at the ground surface, generally indicated at 15, suspended from a drilling tower 16 by means of conventional hoisting block 17 and yoke assembly 18. Power is supplied to the hydraulic motor from a conventional diesel-pump unit (not depicted).

The hydraulic drill motor imparts rotary motion to the drill-string 11 by means of the direct connection to the upper length 19 of the drillstring, at the first tool joint 20, which is of the double-threaded box-and-pin type, depicted in detail in FIGS. I and V, which will be hereinafter described.

The drillstring 11 comprises an outer pipestring 21, and an inner concentric string 22 having an internal bore 23, and co-axially spaced from the outer string to provide an annular outer fluid passage 24. The dual pipestrings 21 and 22 are made up respectively of pipestands of substantially corresponding ov'erall lengths. The outer pipe 21 of each stand is provided with conventional box-and-pin tool joint members'25 and 2, FIG. I, welded at its upper and lower ends respectively; similarly, the inner pipe member 22 is provided with box-and-pin joint members, one of such inner pipe pin joint members being designated 22, positioned adjacent the corresponding box-and-pin joint members 25 and 26 of the outer pipe 21. As illustrated in FIG. V, the inner and outer pipe box-and-pin joints are each terminally threaded at 22" and 25' respectively to form a thread series in each joint having equal pitch threads machined on a conic surface having small diameterreducing taper towards the ends of the pin sections of the joints. The box-and-pin type tool joints are well known in the drilling industry, and achieve structural and shape characteristics which make them of peculiar adaptability to the dual composite drillstring when used with gaseous circulating media, by reason of both physical strength and relatively unrestricted passage areas within the joint. The construction of the dual concentric drillpipe which may be used with the embodiment of the transfer sub of this invention is described in detail in Chapman U.S. application Ser. No. 207,758, filed Dec. 14, 1971, on DUAL CONCENTRIC DRILL- PlPE.

Positioned between the bottom stand of the drillpipe ll and the downhole percussion motor 112 is the transfer sub of this invention, generally designated 27, in FIG. I, the function of which is firstly to deliver the downstream flow of energized fluid from the annulus 24 of the drillstring ill to the central passge of the drillbit 13, and secondly, to transfer the exhausted air and entrained cuttings from the bottom of the bore 14, which move upwardly in the annular space between the exterior of the percussion motor 12 and the wall of the borehole, into the central passage 23 of the interior concentric pipe 22 of the drillstring 11 for delivery to the ground surface, thus. effecting a cross-over of the two separate streams.

Describing the transfer sub in detail, reference may 7 be had to FIG. II, which depicts the transfer sub in three main parts, these being the body portion 28, upper tool joint section 29 and a lower tool joint section 30.

The body portion 28 is generally cylindrical in form, and defines an inner bore 31 having a blind bottom 32, and a plurality of longitudinal drillings 33, extending lengthwise throughout the body portion 28. The longitudinal drillings 38 are formed in two groups, in crosssection, so that each group will subtend an arc of approximately 90, thereby defining two substantial crosssectional areas of the body portion 28, which are desirably diametrically opposite in cross-section, which will be undrilled by the drillings 33, as depicted in FIG. III, for reasons which will hereinafter appear. In the embodiment of the apparatus described herein, the drillings 33 are six in number, in two groups of three, radially spaced to subtend arcs of 30l between the centres of adjacent drillings, and are of a combined crosssectional area substantially equal to the cross-sectional area of the annular space 24 in the drillpipe 21, so that no significant undue restriction in downward flow of energized drilling fluid is developed in the transfer sub.

It will be apparent, from FIGS. III and TV, that the passages defined by the drillings 33 are isolated from the bore M, by the wall sections 34 of the body portion 28.

A plurality of side entry ports 35 are machined through the walls of the body portion 28, at positions intermediate the two groups of longitudinal drillings 33, as depicted in FIG. III. The ports 35 are formed with their adjacent longitudinal side walls 36 and 37 respectively, generally tangential to the interior bore circle 38 defined by the walls of the interior bore SI of the transfer sub.

The opening 39 defined by the ports 35 on the outer surface of the body portion 28 is generally rectangular in configuration, as depicted in FIG. II, having converg ing side walls 36 and 37, terminating in the opening 40 at the inner bore circle 38. For clockwise rotation of the drillstring ill, as is the conventional practise in the drilling industry, the ports 35 will be relieved at the intersection 35 of the longitudinal side wall 36 (the leading side wall), with the outer surface of the body portion 28, as depicted in FIG. III, in order to facilitate entry of rock cuttings into the ports. It is correspondingly desirable that there be no relieving of the following side wall 37 at its intersection with the outer surface of the body portion 28, as depicted in FIG. III. The face of the following side wall 37 is hard-surfaced in order to resist the abrasion produced by the impact of rock cuttings.

The bottom wall 41 and the top wall 42 of the port 35 are each upwardly inclined, as depicted in FIG. IV, at an angle of approximately 45, in order to direct the stream of exhaust air and cuttings upwardly into the bore 3ll of the transfer sub. In sizing the ports 35, it has been found that satisfactory results are produced for most sub-surface conditions when the width of the port entry opening wand the port discharge opening 40 results from the port side walls 36 and 37 being each substantially tangential to the inner bore circle 38 and at an intersecting angle with each other of the order of 62", as depicted in FIG. III. This results in a port passage having converging side walls and the port entry opening 39 being of substantially less width than the port discharge opening 40, as depicted in FIG. III, thereby rejecting any oversized rock chips from the upstream fluid flow within the system.

In the embodiment of the transfer sub described herein, a total of two ports are depicted on the body portion 28, positioned in opposed and vertically staggered relationship thereon. It will be understood that depending on circumstances, the numbers or ports may be increased to six or eight, by increasing the length of the body portion 28.

The tangential aspect of the ports 35 as they comm unicate with the interior bore 31, and their upward inclination, will combine to produce an upwardly directed vortex in the upstream exhaust air within the interior bore 311, for purposes which will become apparent as this specification proceeds.

The body portion 28is reduced in external diameter at its upper end 43, in order to accommodate the engaging inner surface 44 of the upper tool joint section 29, as depicted in FIG. IV. The outer box joint 45 is internally machined at its lower end 47, for a press-fit onto the upper end 43 of the body section 28, and is fillet welded at 47' to the body section 28. The upper tool joint section 28 comprises an outer tubular member 45 and an inner concentric tubular member 46, each threaded internally, to form a double box joint, as depicted in FIGS. II and IV.

A tool joint connector tube member 48, tubular in form, is secured to the upper end 43 of the body portion 28, by machining out'an annular cylindriform recessed surface 49 within the bore 31 of the body portion 28 at its upper end 43, as depicted in FIGS. and IV, the tool joint connector section being permanently secured as by the weld 50 to the body portion 28. Desirably, the internal bore of the tool joint connector member 48 will be equal to the internal bore 31 of the body portion 28, so as to provide unrestricted upward passage of the exhaust air and cuttings. The tool joint connector member 48 is provided with external threads 51 at its upper end 52, FIG. IV, extending only partially down the outer cylindriform surface of the tool joint connector member 48, so that at least a portion thereof 53 is provided with a smooth outer surface for engagement with an O-ring seal of the inner tool joint 46, which will next be described.

Positioned internally concentrically within the outer box joint 45 by means of radial lugs 54, is an inner box joint 46, which is of an external diameter such that an annular space 55 is defined between the outer wall of the inner box joint section 46 and the internal wall of the exterior box joint section 45, as depicted in FIG. IV. The lugs 54 are desirably four in number, radially positioned within the annular space 55, and staggered longitudinally axially for additional support of the inner box joint 46 and are initially fillet welded to the interior box joint 46, and after machining for sizing to the internal wall of the exterior box joint section 45, are drilling welded to the outer box joint 45 by means of drillings 56 and plug welds therein.

The interior box joint 46 is internally threaded at its lower end 57 to accommodate the external threads 51 on the tool joint connector member 48, previously described. An O-ring groove 58 and O-ring seal 59, FIG. IV, are positioned below the threaded portion of the lower end 57 of the internal tool joint section 46, to provide a fluid-tight seal between the tool jont section 46 and the tool joint connector member 48.

Internal threads 60, having matching pitch with internal threads 61 of the inner box joint 46, are formed on the upper ends of both internal and external members of the upper tool joint section 29 The relative lengths of the internal and external members 45 and 46 of the upper tool joint section 29 are such that, when assembled, the upper end 62 of the internal tool joint section 46 will be depressed substantially within the upper end 63 of the outer tool section 45, as depicted in FIG. IV, for reasons which will be hereinafter explained.

In assembly of the parts of the transfer sub, the upper tool joint section 29, after make-up of the internal member 46 and the external member 45 by means of the welded radial lugs 54, is threaded as a unit onto the tool joint connector member 48 at the threads 51 of the inner box joint member 46, with the O-ring seal 58, 59 in operative position, and when the threads 51 are fully made-up, the outer box joint is welded at its lower end 47 to the body portion 29, by means of fillet weld 47.

The lower tool joint section 30 is machined from solid stock having an external diameter equal to the external diameter of the body portion 28, so that when the transfer sub is fully assembled, it will present a continuous cylindriform outer surface. The lower tool joint section 30 is drilled concentrically lengthwise to define a longitudinal bore 65, having a cross-sectional area substantially equal to the combined cross-sectional areas of the longitudinal drillings 33 in the body section 28. An entry section 66 is formed at the upper end of the lower tool joint section 30, to provide communication between the bore 65 and the longitudinal drillings 33, the entry section having downwardly converging side walls 67, and an interior bore 68, equal to the diameter 69 of the circle defined by the drillings 33 at their points of maximum distance from the geometric centre of the cross-section of the body portion 28, as depicted in FIG. III. The lowerend 70 of the bore 65 comprises a box joint, having a downwardly increasing internal diameter, and interior threads 71, to accommodate the thread-coupled pin joint on the upper end of the downhole percussion motor 12, as depicted in FIG. I. The lower tool joint section 30 is secured to the body section 28 as by fillet weld 72.

The structure for coupling of the transfer sub 27 with the distal end of the dual string drillpipe 11 will now be described. The outer pin joint member 25, FIG. V, of the drillpipe 11 is designed for sealing with the upper end of the transfer sub 27 by full make-up of the registering outer box-and-pin joints, the shoulder 25" of the outer pipe pin joint 25 being machined for metal-tometal contact with the butt end 63 of the box joint 45 of the transfer sub, as depicted in FIG. II. The inner pipe seal is accomplished by the combination of the threaded pin joint 22, FIG. V, of the inner pipe 22 with the threaded box joint 61, FIG. II, of the transfer sub 27, and additionally the O-ring 22", FIG. V, of the inner pipe 22 of the drillpipe, which registers against the inner bore 61'159 of the transfer sub box joint 46, FIG. II. Adequate thread length is provided on the threads of the inner pipe pin joint 22' so that full makeup of the outer pipe pin-and-box joint will occur before full make-up of the inner pin-and-box joint occurs, thereby assuring full sealing of the outer pipe pin-andbox joint, the inner joint sealing thereof being completed by the O-ring 22" of the inner pipe with the rigistering cylindriform inner surface 61 of the inner box joint 46 of the transfer sub.

A conventional downhole percussion motor generally indicated at 12, typically of the 'piston-and-anvil type, is thread-connected to the lowerend of the transfer sub 27, as depicted in FIG. I, and a percussion bit 13 is secured to the lower end of the percussion motor,

for contact with the rock at the bottom of the bore hole.

The upward flow of cuttings into the transfer sub is achieved by maintaining gas pressure in the annular area between the outer pipe 21 and the bore 14 by way of a surface seal assembly depicted generally in FIG. I at 73. This surface seal assembly consists of a conventional stuffing box member 74, welded to a short length of surface casing 75,'cemented in position at the surface as at 76, in FIG. I. The surface seal assembly is provided with a small downward air flow by means of the air pressure connection 77, FIG. I.

A cuttings flow gooseneck connection 78 is connected to the top discharge outlet of the hydraulic motor 15, and connected to a cuttings recovery hose 79, leading to a cuttings recovery container (not depicted).

Compressed air is provided for the operation of the downhole apparatus by means of an air line 80, and stuffing box depicted generally at 81, communicating with the annular space 24 between the outer and inner pipecomponents of the dual pipe string.

OPERATION In considering the operation of the apparatus, the equipment will be assumed to be set up as illustrated in FIG. I, with a compressor providing compressed air or other gas to the air line 80 and stuffing box 81 where the gas will flow downwardly through the annular bore 24, through the full length of the drillstring, passing into the transfer sub 27 through the annular passage 55, FIG. IV, of the upper tool section 29, into the longitudinal passages 33 of the body section 28, and then directed through the bore 65 of the lower tool joint section 30 into the connected downhole percussion motor 12, thereby operating the motor for reciprocating percussion action of the bit 13 against the rock face of the bore hole 14. The combined rotary and percussion action of the bit on the rock face operates to rapidly penetrate the formation, reducing the rock encountered to chips and cuttings of a size sufficient to enable them to be swept up by the exhaust gas from the motor 12, discharged centrally from the face of the bit 13, radially outwardly across the bottom of the bore hole, and upwardly in the annular space between the downhole percussion motor 12 and the walls of the bore hole, to the entry ports 39 in the transfer sub 27, for delivery to the internal bore 31 of the transfer sub in upwardly inclined helical fashion, induced by the tangential configuration of the ports 39 and the upward inclination of the lower and upper walls 41 and 42 of the port passage 35. The upwardly directed swirl induced by the multiple port passages 35 retains the entrained rock cuttings in suspension throughout their upward travel in the interior bore 23 of the drillstem 11, until they reach the ground surface, where they are delivered through the gooseneck fitting 78 to the cuttings recovery hose 79, where the cuttings are collected for examination.

As previously referred to in this disclosure, the downhole percussion motor 12 may be removed, when conditions warrant, and the bit 13 coupled directly to the end of the lower tool joint section 30 of the transfer sub 27, which is in turn coupled to the lowermost stand of dual-wall concentric drillpipe, so that the drilling apparatus is then operated as a rotary drill, instead of a rotary-percussion drill. Downhole conditions which may warrant the elimination of the percussion motor are, for example, in upper sections of the hole when drilling through glacial till; and when formation water is en countered in relatively large volume and it therefore becomes necessary to change the drilling fluid from air to liquid.

In the drilling of deeper holes, it has been found that, through the design of the drillpipe and transfer sub, in which undue pressure losses have been avoided by maintaining cross-sectional areas throughout the flow passages, it is possible to maintain within the annular space 24 of the drillstem and the internal bore 23 of the drillstem, a sufficiently high velocity of gas flow to operate the downhole motor 12, and to assure continued entrainment of the cuttings throughout the course of the gas flow to the surface of the ground.

From the foregoing it will be understood that during the drilling operation, the gaseous fluid circulation is confined to the dual passages within the drillstring, except immediately adjacent the percussion motor 12 and bit 13, and as a result, no fluid circulation flow occurs within the bore hole 14 outside of the drillstring 11, for contact with the wall of the bore hole. As a consequence, the bore hole walls and rock formation at the bit remain in a relatively uncontaminated condition, thereby assuring that the cuttings produced at the surface correctly represent the composition of the structure being penetrated by the bit at any given time.

If for any reason, such asplugging by congestion of the upstream flow in any of the cuttings passages, it becomes necessary to reverse the circulation of the fluid through the drillstring, the compressor discharge'may be disconnected from line 80 and connected to the cuttained until the obstruction is removed.

Reference has been made previously to the importance of the transfer sub: make-up-andconstruction, to ensure thatthe cross-sectional areas-of the flowpassages within the transfersub provide minimum restriction to the flow of fluid downwardly and the exhaust fluid and entrained cuttings upwardly. In the apparatus of this invention, this has been accomplished by the design of the ports 35, the tool jointconnector member 48, the upper tool joint section 29withthe radial lugs 54 presenting minimal obstruction to the downward flow of drilling fluid, and the longitudinal drillings 33 within the body section .28. At the same time, rigid construction for delivery of torque tothebit, and physical strength to resist the impact stresses developed by the downhole percussion motor 12, is: developed within the transfer sub, by means of the construction described.

When unacceptable wear has occurred. at the threaded joints of the tool jointsat either endof the transfer sub, either joint may be replaced by. cutting the weld between the body section 28mand:the-ass0ciated joint, and removing the worn joint for replacement; breaking of the welds 56 securing theradial lugs 54l-is unnecessary in replacementof the upper tool joint section 29, since the cutting of, the fillet weld47' permits the entire upper tool joint section 29to. be removed from the body section 28. by uncoupling the thread jointSl interconnecting the tool' jjoint connectormember 48 with the inner box joint member. 46.

Since various modifications canbe made inthe apparatus of this invention, as hereinabove described, and in many apparently widely differingembodiments of the same made withinithespirit andscope ofthe claims without departing from such spirit and scope, it is intended that allmatters inthe accompanying specificaa tions shall be interpreted as illustrative only and tnot in a limiting sense.

What I claim as my invention is:

1. A fluid delivery and transfer unit for use with a dual string drillpipe havingseparate fluid passages for a downstream flow of energized fluid and for a combined upstream flow of exhaust fluid andentrained cuttings returns, and a downholefluid-operated percussion motor having a downstream: inlet fluid passage, said fluid delivery and transfer unit being; adapted for removable attachment to the lower end of said drillpipe at its first end and to said percussion motor at the second end of said fluid'delivery and transfer unit, comprising, in combination:

i. an elongated metallic cylinder having downstream, inlet and upstream outlet fluid passages at said-first end thereof adapted for separate communication. with said downstream and upstream fluid passages in said dual string drillpipe and having; a single downstream outlet passage at said second end thereof adapted for communication with the downstream inlet fluid passage of saiddownhole percussion motor for delivery of energized fluid thereto;

ii. ports means defined in. the exterior of'said cylinder communicating with the upstream outlet fluidpassageat said first end of said elongated cylinder;

iii. longitudinal passage means defined withinisaid elongated cylinder communicating with said down stream inlet fluid passage at said first end of said elongated cylinder and with. downstream outlet passage at said second end of said elongated cylin der;

iv. first coupling means for removable connectionof said elongated cylinder at said first end thereof. to the distal end of said dual string drillpipe;

v. second coupling means for removable connection of said elongated cylinder at said second end thereof to said downhole percussion motor.

2. A fluid delivery and transfer unit as disclosed in claim l wherein said first coupling means comprises:

(i) a tubular outer pipe box joint member secured to said first end of said cylinder coaxial therewith and having internal threads thereon;

(ii) a tubular inner pipe box joint member secured to said first end of said cylinder coaxial with and spaced from said outer pipe box joint member and having internal threads thereon, said outer pipe box joint member and said inner pipe box joint member thereby defining an annular fluid passage therebetween as said downstream inlet fluid passage and said inner pipe joint member defining a bore therein as said upstream outlet fluid passage.

3. A fluid delivery and transfer unit as disclosed in claim 2 wherein said second coupling means comprises a tubular pin joint member secured to said second end of said cylinder coaxial therewith and having external threads thereon, said tubular pin joint member defining a bore therein as said downstream outlet fluid passage.

4. A fluid delivery and transfer unit for use with a dual string drillpipe having separate fluid passages for a downstream flow of energized fluid and for a combined upstream flow of exhaust fluid and intrained cuttings returns, and a downhole fluidoperated percussion motor having a downstream inlet fluid passage, said fluid delivery and transfer unit being adapted for removable attachment to the lower end of said drillpipe at its first end and to said percussion motor at the second end of said fluid delivery andtransfer unit, comprising in combination:

(i) an elongated metallic cylindriform body portion having a longitudinal cylindriform body portion central bore communicating with an upstream fluid discharge outlet at a first end of said body portion and terminating in a blind bottom adjacent a second end of said body portion and thereby defining body portion sidewalls between said central bore and the external cylindriform surface of said body portion;

(ii) longitudinal downstream fluid passage means extending lengthwise through said body portion and isolated from said central bore;

(iii) a tubular outer pipe box joint member secured to said first end of said body portion coaxial therewith and having internal threads thereon;

(iv) a tubular inner pipe box joint member secured to said first end of said body portion coaxial with and spaced from said outer pipe box joint member and having internal threads thereon, said inner pipe box joint member defining an upstream fluid discharge outlet and a central bore communicating with said upstream fluid discharge outlet and with said body portion central bore, said outer pipe box joint member and saidiiiner pipe box joint member thereby defining an annular downstream fluid passage therebetween;

(v) a tubular pin joint member secured to said second end of said body portion coaxial therewith and having external threads thereon, said tubular pin joint member defining a bore therein as said downstream outlet fluid passage, said outlet fluid passage communicating with said longitudi- 5. A fluid delivery and transfer unit as disclosed in claim 4 in which said longitudinal downstream fluid passage means comprise a plurality of longitudinal drillings extending lengthwise through said body portion sidewalls. """Kf/Tfiliiii' delivery and transfer unit as disclosed in claim 5 in which said longitudinal drillings are grouped for cross-sectional location withinsaid side walls so that a substantial portion of the cross-sec tional area of said sidewalls is unpenetrated by said drillings and is thereby available to accommodate said port means.

7. A fluid delivery and transfer unit as disclosed in claim 5 in which said longitudinal drillings are positioned for cross-sectional location within said sidewalls so as to define two groups of drillings, the walls of the most remote pair of members of each such group sub-tending an arc of the order of 8. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear crosssectional configuration having substantially vertical,

port passage sidewalls each lying in a plane substantially. tangential to the cylindriform body portion central bore and defining a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore.

9. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear crosssectional configuration having substantially vertical port passage sidewalls each lying in a plane substantially tangential to the cylindriform body portion central bore and having substantially planar port passage bottom and top walls each inclining upwardly and inwardly towards said body portion central bore and thereby defining with said port passage sidewalls a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore.

10. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear crosssectional configuration having substantially vertical port passage sidewalls each lying in a plane substantially tangential to the cylindriform body portion central bore and defining a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore, said port entry opening and said port discharge opening having widths such that the arcs defined by the intersection of said port passage bottom and top walls with said external cylindriform surface of said body portion, and the intersection of said port passage bottom and top walls with said body portion central bore, each subtend approximately 62. 1 1 A fl uid delivery andtransfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear crosssectional configuration having substantially vertical port passage sidewalls each lying in a plane substantially tangential to the cylindriform body portion central bore and having substantially planar port passage bottom and top walls each inclining upwardly and inwardly towards said body portion central bore and merets defifiing with said port passage sidewalls a generally rectilinear port entry opening on the outer cylindriform surface of said body' portion and a generally rectilinear port discharge opening with said body portion central bore, said port entry opening and said port discharge opening having widths such that thearcs-defined by the intersection of said port passage bottom and top walls with said externalcylindriform surface of said body portion, and the intersection of said port passage bottom and top walls with said body portion central bore, each subtend approximately 62.

12. A fluid delivery and transfer unit for use with a dual string drillpipe having separate fluid passages for a downstream flow of energized fluid and for a combined upstream flow of exhaust fluid and entrained cuttings returns defined by a pair of inner and outer concentric pipe members disposed in coaxial spaced relationship, such pipe members each terminating in an externally-threaded pin joint member similarly disposed in coaxial spaced relationship and having substantially co-planar distal ends, said fluid delivery transfer unit being adapted for removeable thread-coupled attachment to the lower end of said dual string drillpipe, comprising in combination: (i) an elongated metallic cylindriform body portion having a longitudinally extending cylindriform body portion central bore communicating with an upstream fluid discharge outlet at a first end of said body portion and terminating in a blind bottom adjacent a second end of said body portion the thereby defining body portion sidewalls between said central bore and the external cylindriform surface of said body portion; (ii) longitudinal downstream fluid passage means extending lengthwise through said body portion and isolated from said central bore;

(iii) a tubular outer pipe box joint member secured to said first end of said body portion coaxial therewith and having internal threads thereon adapted to register with the external threads on said pin joint member of said outer concentric pipe member of said dual string drillpipe;

(iv) a tubular inner pipe box joint member secured to said first end of said body portion disposed coaxially with and spaced from said outer pipe box joint member so that the distal end of said inner pipe box joint member is substantially depressed below the distal end of said outer pipe box joint member, and having internal threads thereon adapted to register with the external threads on said pin joint member of said inner concentric pipe member of said dual string drillpipe, said inner pipe box joint member defining an upstream fluid discharge outlet and a central bore communicating with said upstream fluid discharge outlet and with said body portion central bore, said inner pipe box joint member and said outer pipe box joint member thereby defining an annular downstream fluid passage therebetween;

(v) a tubular pin joint member secured to said second end of said body portion coaxial therewith and having external threads thereon, said tubular pin joint member defining a bore therein as said downstream outlet fluid passage, said outlet fluid passage communicating with said longitudinal downstream fluid passage means extending lengthwise through said body portion;

(vi) port means defined in said body portion sidewalls and isolated from said longitudinal downstream fluid passage means and extending through said sidewalls for communication with said body portion central bore.

13. A fluid delivery and transfer unit as disclosed in claim 12 additionally comprising:

(i) a tubular tool joint connector member secured to said body portion at the first end thereof and coaxial therewith, and having thread means on the distal end thereof for threaded interconnection with said inner pipe box joint member, and

(ii) a plurality of metal lugs radially spanning said annular downstream fluid passage and securing said outer pipe box joint member to said inner pipe box joint member.

14. A fluid delivery and transfer unit as disclosed in claim 12 additionally including resilient sealing means positioned on the interface between said tool joint connector member and said inner pipe box joint 

1. A fluid delivery and transfer unit for use with a dual string drillpipe having separate fluid passages for a downstream flow of energized fluid and for a combined upstream flow of exhaust fluid and entrained cuttings returns, and a downhole fluid-operated percussion motor having a downstream inlet fluid passage, said fluid delivery and transfer unit being adapted for removable attachment to the lower end of said drillpipe at its first end and to said percussion motor at the second end of said fluid delivery and transfer unit, comprising, in combination: i. an elongated metallic cylinder having downstream inlet and upstream outlet fluid passages at said first end thereof adapted for separate communication with said downstream and upstream fluid passages in said dual string drillpipe and having a single downstream outlet passage at said second end thereof adapted for communication with the downstream inlet fluid passage of said downhole percussion motor for delivery of energized fluid thereto; ii. ports means defined in the exterior of said cylinder communicating with the upstream outlet fluid passage at said first end of said elongated cylinder; iii. longitudinal passage mEans defined within said elongated cylinder communicating with said downstream inlet fluid passage at said first end of said elongated cylinder and with downstream outlet passage at said second end of said elongated cylinder; iv. first coupling means for removable connection of said elongated cylinder at said first end thereof to the distal end of said dual string drillpipe; v. second coupling means for removable connection of said elongated cylinder at said second end thereof to said downhole percussion motor.
 2. A fluid delivery and transfer unit as disclosed in claim 1 wherein said first coupling means comprises: i. a tubular outer pipe box joint member secured to said first end of said cylinder coaxial therewith and having internal threads thereon; ii. a tubular inner pipe box joint member secured to said first end of said cylinder coaxial with and spaced from said outer pipe box joint member and having internal threads thereon, said outer pipe box joint member and said inner pipe box joint member thereby defining an annular fluid passage therebetween as said downstream inlet fluid passage and said inner pipe joint member defining a bore therein as said upstream outlet fluid passage.
 3. A fluid delivery and transfer unit as disclosed in claim 2 wherein said second coupling means comprises a tubular pin joint member secured to said second end of said cylinder coaxial therewith and having external threads thereon, said tubular pin joint member defining a bore therein as said downstream outlet fluid passage.
 4. A fluid delivery and transfer unit for use with a dual string drillpipe having separate fluid passages for a downstream flow of energized fluid and for a combined upstream flow of exhaust fluid and entrained cuttings returns, and a downhole fluid-operated percussion motor having a downsream inlet fluid passage, said fluid delivery and transfer unit being adapted for removable attachment to the lower end of said drillpipe at its first end and to said percussion motor at the second end of said fluid delivery and transfer unit, comprising, in combination: i. an elongated metallic cylindriform body portion having a longitudinal cylindriform body portion central bore communicating with an upstream fluid discharge outlet at a first end of said body portion and terminating in a blind bottom adjacent a second end of said body portion and thereby defining body portion sidewalls between said central bore and the external cylindriform surface of said body portion; ii. longitudinal downstream fluid passage means extending lengthwise through said body portion and isolated from said central bore; iii. a tubular outer pipe box joint member secured to said first end of said body portion coaxial therewith and having internal threads thereon; iv. a tubular inner pipe box joint member secured to said first end of said body portion coaxial with and spaced from said outer pipe box joint member and having internal threads thereon, said inner pipe box joint member defining an upstream fluid discharge outlet and a central bore communicating with said upstream fluid discharge outlet and with said body portion central bore, said outer pipe box joint member and said inner pipe box joint member thereby defining an annular downstream fluid passage therebetween; v. a tubular pin joint member secured to said second end of said body portion coaxial therewith and having external threads thereon, said tubular pin joint member defining a bore therein as said downstream outlet fluid passage, said outlet fluid passage communicating with said longitudinal downstream fluid passage means extending lengthwise through said body portion; and vi. port means defined in said body portion sidewalls and isolated from said longitudinal downstream fluid passage means and extending through said sidewalls for communication with said body portion central bore.
 5. A fluid delivery and transfer unit as disclosed in claim 4 in which said longitudinal downstream fluid Passage means comprise a plurality of longitudinal drillings extending lengthwise through said body portion sidewalls.
 6. A fluid delivery and transfer unit as disclosed in claim 5 in which said longitudinal drillings are grouped for cross-sectional location within said sidewalls so that a substantial portion of the cross-sectional area of said sidewalls is unpenetrated by said drillings and is thereby available to accommodate said port means.
 7. A fluid delivery and transfer unit as disclosed in claim 5 in which said longitudinal drillings are positioned for cross-sectional location within said sidewalls so as to define two groups of drillings, the walls of the most remote pair of members of each such group sub-tending an arc of the order of 90*.
 8. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear cross-sectional configuration having substantially vertical port passage sidewalls each lying in a plane substantially tangential to the cylindriform body portion central bore and defining a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore.
 9. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear cross-sectional configuration having substantially vertical port passage sidewalls each lying in a plane substantially tangential to the cylindriform body portion central bore and having substantially planar port passage bottom and top walls each inclining upwardly and inwardly towards said body portion central bore and thereby defining with said port passage sidewalls a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore.
 10. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear cross-sectional configuration having substantially vertical port passage sidewalls each lying in a plane substantially tangential to the cylindriform body portion central bore and defining a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore, said port entry opening and said port discharge opening having widths such that the arcs defined by the intersection of said port passage bottom and top walls with said external cylindriform surface of said body portion, and the intersection of said port passage bottom and top walls with said body portion central bore, each subtend approximately 62*.
 11. A fluid delivery and transfer unit as disclosed in claim 5 in which said port means comprise port passages each having generally rectilinear cross-sectional configuration having substantially vertical port passage side walls each lying in a plane substantially tangential to the cylindriform body portion central bore and having substantially planar port passage bottom and top walls each inclining upwardly and inwardly towards said body portion central bore and thereby defining with said port passage sidewalls a generally rectilinear port entry opening on the outer cylindriform surface of said body portion and a generally rectilinear port discharge opening with said body portion central bore, said port entry opening and said port discharge opening having widths such that the arcs defined by the intersection of said port passage bottom and top walls with said external cylindriform surface of said body portion, and the intersection of said port passage bottom and top walls with said body portion central bore, each subtend approximately 62*.
 12. A fluid delivery and transfer unit for use with a dual string drillpipe haVing separate fluid passages for a downstream flow of energized fluid and for a combined upstream flow of exhaust fluid and entrained cuttings returns defined by a pair of inner and outer concentric pipe members disposed in coaxial spaced relationship, such pipe members each terminating in an externally-threaded pin joint member similarly disposed in coaxial spaced relationship and having a substantially co-planar distal ends, said fluid delivery transfer unit being adapted for removeable thread-coupled attachment to the lower end of said dual string drillpipe, comprising in combination: i. an elongated metallic cylindriform body portion having a longitudinally extending cylindriform body portion central bore communicating with an upstream fluid discharge outlet at a first end of said body portion and terminating in a blind bottom adjacent a second end of said body portion and thereby defining body portion sidewalls between said central bore and the external cylindriform surface of said body portion; ii. longitudinal downstream fluid passage means extending lengthwise through said body portion and isolated from said central bore; iii. a tubular outer pipe box joint member secured to said first end of said body portion coaxial therewith and having internal threads thereon adapted to register with the external threads on said pin joint member of said outer concentric pipe member of said dual string drillpipe; iv. a tubular inner pipe box joint member secured to said first and of said body portion disposed coaxially with and spaced from said outer pipe box joint member so that the distal end of said inner pipe box joint member is substantially depressed below the distal end of said outer pipe box joint member, and having internal threads thereon adapted to register with the external threads on said pin joint member of said inner concentric pipe member of said dual string drillpipe, said inner pipe box joint member defining an upstream fluid discharge outlet and a central bore communicating with said upstream fluid discharge outlet and with said body portion central bore, said inner pipe box joint member and said outer pipe box joint member there by defining an annular downstream fluid passage therebetween; v. a tubular pin joint member secured to said second end of said body portion coaxial therewith and having external threads thereon, said tubular pin joint member defining a bore therein as said downstream outlet fluid passage, said outlet fluid passage communicating with said longitudinal downstream fluid passage means extending lengthwise through said body portion; vi. port means defined in said body portion sidewalls and isolated from said longitudinal downstream fluid passage means and extending through said sidewalls for communication with said body portion central bore.
 13. A fluid delivery and transfer unit as disclosed in claim 12 additionally comprising: i. a tubular tool joint connector member secured to said body portion at the first end thereof and coaxial therewith, and having thread means on the distal end thereof for threaded interconnection with said inner pipe box joint member, and ii. a plurality of metal lugs radially spanning said annular downstream fluid passage and securing said outer pipe box joint member to said inner pipe box joint member.
 14. A fluid delivery and transfer unit as disclosed in claim 12 additionally including resilient sealing means positioned on the interface between said tool joint connector member and said inner pipe box joint member. 